Transcript

Norman Swan: Good morning and welcome. Today on the Health Report the latest research on what to do if someone has a cardiac arrest in front of you and you don't fancy the idea of mouth to mouth respiration; Australian research into an increasingly common cause of cardiac arrest; preventing weight gain in young mothers, and your hips and your heart.

A couple of years ago we covered New Zealand research which suggested that calcium supplements taken by themselves to prevent osteoporosis may actually be associated with an increased risk of heart attacks. It was enormously controversial at the time but now the Auckland researchers have done a much bigger analysis to see whether the risk is really there from these commonly swallowed supplements.

Ian Reid is Professor of Medicine and Endocrinology at the University of Auckland.

Ian Reid: We started with a hypothesis that calcium might be good for heart disease because we'd previously shown that people who take calcium have better blood cholesterol profiles and we and other groups had shown that calcium supplements have a beneficial effect on blood pressure, a small effect but a beneficial one. So we carried out a randomised controlled trial two years ago to look specifically at this issue to see whether heart attacks were less or more frequent in people who were randomised to calcium. And we were surprised in that study of post-menopausal women to find that there was actually an increase in the risk of heart attacks than there was in the women who were randomised to calcium.

And usually when you find a suggestive but not conclusive finding in a trial the answer is to do a bigger, longer trial and prove it once and for all. But that's not really ethically acceptable or practical when your hypothesis says that this particular intervention can cause harm. And so we decided to try and gather the maximum amount of data possible from trials that have already been carried out. So we wrote to everyone who had carried out a trial of calcium in comparison with placebo and asked them whether they could possibly access data on heart attacks and strokes and death; and fortunately in more than 90% of the subjects involved in those trials that kind of data is available to some extent. So this meta-analysis is a bringing together of that data from eleven different trials around the world.

Norman Swan: But not all of those trials would have looked primarily at the influence of heart attacks that have been doing calcium supplements for osteoporosis and things like that.

Ian Reid: That's right, all of them -- none of them had heart attacks as the primary focus and so the heart attack data and the stroke data is just being collected as part of the safety data. So it doesn't have the same rigour that the fracture data had, which would have been very carefully documented. So, if anything, that might tend to cause you not to find an effect that's there rather than introduce an effect that's not there.

Norman Swan: When you brought it all together how many people did it total?

Ian Reid: The total data is on about 11,900 people and the average duration of the study is four years, so we've got almost 50,000 patient years of data of subjects randomised to calcium or to placebo. The great majority are post-menopausal women but there are some studies of men included. The average age of the people in the study is in their early 70s, so this is an elderly population and that's an important qualification because it doesn't necessarily transfer to 30-year-old or 40-year-olds who might want to take calcium supplements.

Norman Swan: And the average dose of calcium?

Ian Reid: Most of these studies were using a dose of a gram a day, some used only 500mgs but the average dose was close to a gram a day. And that's pretty much what's used in clinical practice.

Norman Swan: What did you find?

Ian Reid: All of the major studies showed a 20% to 30% increase in the risk of heart attack and when you pulled all those data together overall there was a 30% increase in the risk of heart attack. There was a similar adverse trend in relation to strokes but that was not statistically significant. And what we can calculate is that if 1,000 people are treated with calcium for five years there would be 14 more heart attacks in the calcium group, 10 more strokes and 13 more deaths balanced against 26 fewer fractures. So it appears that use of calcium is associated with 37 more adverse events than 26 fewer fracture events. So we think this really says that the balance is negative.

Norman Swan: There are a couple of things that you do as a cross-check, just as a reality check. One is more calcium -- more heart attacks, was there a dose effect?

Ian Reid: We haven't got a large number of different doses so that is not something that we can easily address from this data base.

Norman Swan: The other reality check is is there a plausible biological mechanism whereby calcium could be having this effect?

Ian Reid: We think there is, for instance in patients with kidney failure who are on dialysis and in patients who have milder degrees of kidney failure not requiring dialysis it's quite clear from clinical trials that the use of calcium supplements increases the risk of either dying or accelerates the rate of vascular calcification and vascular damage. The second clinical cross-check is that we know when people take calcium supplements as opposed to taking food calcium that their blood calcium levels rise over the following few hours and often wind up setting very near the upper end of the normal range for blood calcium. And there's quite a lot of epidemiological data showing that if you just look at normal populations and compare cardiovascular event rates and vessel wall thickness and vessel wall damage and mortality in relation to base line blood calcium levels, people who habitually sit with blood calcium levels near the top of the normal range are more likely to have heart attacks, more likely to have damaged arterial walls and more likely to die than other people in that population who sit in the lower part of the normal range. So that gives some credibility to this finding.

If you start doing studies in the laboratory then there are studies that demonstrate that if you expose the cells from blood vessels to higher concentrations of calcium you see more deposition of calcium into the walls and that's thought to be one of the mechanisms whereby heart attacks are caused.

Norman Swan: Yet diets that are high in calcium don't seem to cause a problem?

Ian Reid: No they don't and our explanation for that, or our hypothesis related to that is that when you take a meal that's rich in calcium your blood calcium level hardly changes at all and we believe that that's because the protein and the fat that are part of that meal slow the rate of absorption. So a meal very gradually releases its calcium into the circulation whereas when you take a calcium supplement you get an abrupt change in blood calcium level which lasts for quite a few hours.

Norman Swan: And what happens when you take nutraceuticals, you know milk that has been fortified with calcium which is effectively you are drinking a calcium supplement, does that affect your calcium levels that much?

Ian Reid: You get some change in calcium but I mean there are some studies that have been done with calcium fortified milk and the change in blood calcium that they produce is about a fifth of what you get from taking the same amount of calcium in a tablet form.

Norman Swan: And how sure are you that these people actually had heart attacks, were they well diagnosed?

Ian Reid: Well yes they were, the majority of the events have been adjudicated and we find exactly the same trends in the adjudicated data bases as we do in those where we were not able to adjudicate them.

Norman Swan: And the same risk in men as in women?

Ian Reid: As far as we can tell.

Norman Swan: A lot of people listening who are on calcium are also on vitamin D and an accompanying editorial to this in the British Medical Journal suggested that maybe vitamin D negates some of the negative effects of calcium.

Ian Reid: This particular study has not addressed that. Obviously that's a very important question and so independently of this study we are going on at the present time and looking at whether calcium plus vitamin D has the same adverse effect and that information we are going to present at conferences in North America later in the year. All I can say at the present time is we don't see a protective effect of vitamin D when we do those analyses.

Ian Reid: That's right, if you're taking 1,000 units of Vitamin D a day that has really no significant effect on blood calcium levels so we would not expect that to be associated with any of these risks.

Norman Swan: What do you think the public health message is here, because it's conflicted, you don't want everybody taking expensive drugs for osteoporosis which have unpleasant side effects, people will feel squeezed into a corner?

Ian Reid: Well I don't think so. I think the reason people take calcium supplements in the first place is to prevent a particular health problem. I think what we can say now is that we lack confidence that we can say to them that that is overall doing them good. So I think most people should talk to their doctors and reconsider whether taking calcium supplements is a particularly useful thing to do. It does leave a gap because the nice thing about calcium was that it was cheap, it was easy to take and it was thought to be safe and it was quite useful in people whose risk of fracture was intermediate. I think what people need to be reviewing with their doctors is what their real risk of having a fracture is and that's now something we can estimate quite accurately and then make a decision based on that as to whether they should be considering taking a medicine to prevent fracture or whether they should just carry on with lifestyle advice and those standard lifestyle recommendations still are relevant, so have a calcium rich diet, don't smoke, keep physically active, don't be too thin...

Norman Swan: And keep your Vitamin D level up.

Ian Reid: Keep you Vitamin D level up through sunshine exposure or through using a moderate supplement. So those things are still very much in place, it's just the one issue of calcium supplements that we're putting a big question mark next to.

Norman Swan: Ian Reid is Professor of Medicine and Endocrinology at the University of Auckland and you're listening to the Health Report here on ABC Radio National with me Norman Swan.

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Comments (8)

Irene Fisher :

05 Aug 2010 9:54:48am

Dear Norman Swan,Such an interesting study but surely the form of calcium is also important here. Most of the calcium we sell in pharmacy is Caltrate (calcium carbonate - chalk, that needs to be in soils so the plants take it up and it becomes converted by photosynthesis into the easiest absorbable form for our bodies, usually as phosphate for the bones, as fluoride for teeth and connective tissue and sulphate for stubborn healing problems). For older people (over 70), often acidity inhibits absorption of calcium, so what about that? Really to get some accuracy with this research, we do need to know the form of calcium used.Thanks for your card, much appreciated. Irene Fisher

Amy Zelmer :

05 Aug 2010 2:18:20pm

In the Report of 2 Aug 2010, Prof Reid remarks, "I think what people need to be reviewing with their doctors is what their real risk of having a fracture is and that's now something we can estimate quite accurately....

Could we have some discussion in a future Report of how this risk can be measured? I've seen a good deal of literature about osteoporosis and the importance of preventing falls, but nothing that I would consider to be an "accurate measure" of the risk of falls. A precise measure would be more helpful than generalities in trying to reduce risk.

robyn :

fruitloop :

08 Aug 2010 4:36:08pm

I am 77 and have been diagnosed with osteoporosis, so Protos (strontium ranelate) was prescribed. I also have heart disease but kidneys OK. Recently my GP ordered a blood test, which showed a low calcium level so she advised calcium supplement. Prof Reid has now left me totally confused about this issue!

cathy :

08 Aug 2010 10:17:11pm

It would be interesting to know if it makes a difference what type of calcium supplement is used. Calcium carbonate is cheap, widely used, and difficult to absorb. Calcium citrate and calcium chelate is more easily absorbed. I wonder if the researchers considered this?

Shirley :

10 Aug 2010 2:34:39pm

Further to cathy's comment also if the studies were done before huge numbers started taking PPIs which is thought may decrease Ca carbonate absorption. There has been a UK correllation of increasing hip fractures with increasing use of PPIs

Susan Kath :

12 Aug 2010 2:21:25pm

I would also be interested in the effect of calcium supplements if taken with a magnesium supplement, given their synergistic relationship and whether this would negated the increased risk of CVD but still support bone health.

Libby :

26 Aug 2010 6:30:40pm

Like others, I am interested if the form of calcium matters or if all calcium is to be avoided. I checked the multivitamin that I take and saw that it includes calcium. I would therefore be very interested in more information about the form of calcium.